The RC model baro dose come in a 4" or 5" also the model RCBT comes in a 4" or 5" you also should size your baro to the size of the chimney your have look at the charts on the Field controls site below

Well when you just spent a couple hours traipsing through the woods in 1.5 foot of snow with case of beer and all you stuff strapped to your back, it's 20 degrees out and takes a good hour to get a nice fire going and some jackass new guy knocks the fire down into the nice wet ground below it we have problem. True story and it happened more than once.

tsb, the Field type M draft damper does not use a Tee. You cut a hole into the pipe and bolt on a shroud that comes with the damper. I'm pretty that with minor modification a 6" would wrap onto and fit a 5" pipe.

This thread has it all. Coal tending theories...humor...even one scary looking homemade baro that scares the hell out of me. The title of the thread should be "Stay away from my fire or I'll kick your ash!"